In the manufacture of semiconductor chips a silicon wafer or other substrate is exposed to a variety of different processes in different processing chambers. The chambers may expose the wafer to plasmas, chemical vapors, metals, laser etching, and various deposition and acid etching processes in order to form circuitry and other structures on the wafer. During these processes, the integrity of the chamber against leaks and impurities is important to ensure that each wafer is the same as the last wafer.
During manufacture and occasionally after a period of use a vacuum chamber for the wafer processing equipment is tested for leaks. The tests verify that a sufficient level of vacuum can be maintained. In some cases, a leak detector, which can be a self-contained mass spectrometer tuned to the mass of helium, is used to scan for the presence of helium within a vacuum chamber. The helium leak rate can indicate that the vacuum chamber requires repair. During manufacture and use water vapor and other molecules may be deposited on the walls of the chamber. These molecules are removed before the chamber is put into service in processing more wafers. In some cases hot cathode mercury discharge tubes are placed into the chamber to break up the molecules.